Lautenberg, the 89-year-old senator who served for almost two decades in the Senate from 1982 through 2001 before returning for a second term in the upper chamber in 2003, will not seek another six-year term.

"I will be traveling to my hometown of Paterson tomorrow to announce that I will not seek re-election in 2014. This is not the end of anything, but rather the beginning of a two-year mission to pass new gun safety laws, protect children from toxic chemicals, and create more opportunities for working families in New Jersey," Lautenberg said in a statement. "While I may not be seeking re-election, there is plenty of work to do before the end of this term and I'm going to keep fighting as hard as ever for the people of New Jersey in the U.S. Senate."

The decision clears the path for Newark Mayor Cory Booker to pursue the Democratic nomination for Senate. Booker, who's built a high national profile with his work as mayor, had provoked some public sniping from Lautenberg for seeming too quick to assume that the longtime senator would necessarily retire when his term is up in 2015.

Another Democrat thought to be eyeing the seat, Rep. Frank Pallone, effusively praised Lauternberg in a statement.

"I have peen proud to serve with Senator Lautenberg and even prouder to call him a friend," he said. "I look forward to continuing to work together in the coming months to continue to address the issues that are important to him and New Jersey. Like all New Jerseyans, I am grateful for his service to our state and our nation."